Microbial water quality in freshwater lakes with different land use.

AIMS: The relationship between land use (undeveloped, cattle grazing, urban), faecal indicator bacteria (FIB) levels and microbial source tracking (MST) marker detection was investigated in lakes created following phosphate mining. METHODS AND RESULTS: Faecal coliforms and enterococci were cultured, and MST markers were detected by PCR [Methanobrevibacter smithii, human polyomaviruses (HPyVs), ruminant, human (HF183) and general Bacteroidales]. FIB levels varied significantly by sampling date and were correlated with antecedent rainfall. FIB levels varied with land use category only in the case of faecal coliform levels in sediments of urban lakes, which were significantly greater than those in undeveloped or cattle-impacted lakes. Ruminant Bacteroidales were detected consistently in cattle-impacted lakes (57%) and rarely in other lakes. HPyVs was the only human source marker detected. CONCLUSIONS: Rainfall was more strongly associated with FIB levels than land use category. The detection frequency of only the ruminant MST marker was associated with land use. SIGNIFICANCE AND IMPACT OF STUDY: Microbial source tracking (MST) can fine-tune the assessment of human health risk from recreational use of inland waters, particularly when similar FIB levels but different surrounding land use and probable impacts exist.

The role of ciliated protozoa in pelagic freshwater ecosystems.

The abundance and biomass of ciliates are both strongly related to lake trophic status as measured by chlorophylla concentrations. Taxonomic replacements occur with increasing eutrophication such that large-bodied forms (predominantly oligotrichs) are progressively replaced by smaller-bodied ciliates (mainly scuticociliates). Highly acidic lakes display a more pronounced dominance of large-bodied forms when contrasted with less acidic lakes of comparable trophy. Community structure of ciliate populations is determined largely by lake trophy with acidic oligotrophic systems being characterized by reduced diversity and species richness compared with hypereutrophic systems. The temporal and spatial distribution of small (< 100µm) ciliate populations is ascribed to lake thermal regimes which provide localized concentrations of food resources. Likewise, in extremely productive lakes, very large (> 100µm) meroplanktonic ciliates enter the water column during midsummer after the development of thermal stratification and associated profundal deoxygenation. Laboratory studies indicate that large zooplankton (crustaceans) are capable of utilizing ciliates as a food source, but there is little direct evidence from field studies documenting this trophic link. Ciliates can be voracious grazers of both bacterioplankton and phytoplankton, and each species has a distinct range of preferred particle size which is a function of both mouth size and morphology. Myxotrophic ciliates may be important components in some plankton communities, particularly during periods of nutrient limitation or after their displacement from the benthos of eutrophic lakes. Evidence regarding the importance of planktonic ciliated protozoa in nutrient regeneration and as intermediaries in energy flow is discussed.